TDA8222 Datasheet, PDF (2/9 Pages) STMicroelectronics – VIDEO & SOUND IF SYSTEM WITH VIDEO AND SOUND SWITCHES

TDA8222
BLOCK DIAGRAM
31
24
23
22
20
Tuner
2
AGC
AGC
5
IF Amplifier
6
Reference
Amplifier
AFC
19
Video
Amplifier
Band Gap
Voltage Reference
9
D.C. Volume
8
Control
17
11
FM
Limiter
Discri
LP Filter
10
16 15
White and
18
Black Noise Inverter
4
14
6dB
12
6dB
Mute
13
21
7
TDA8222
FUNCTIONAL DESCRIPTION
General
The IC consists of the following parts (see block
diagram):
- Three stages gain controlled wide band amplifier
- Quasi-synchronous demodulator
- Video amplifier with white and black noise in-
verter
- AGC circuit which operates on top sync level
- Analog AFC circuit
- FM discriminator
- Mute function
- Video and audio switches
- DC volume control
IF Amplifier
It consists of three cascaded AC coupled differen-
tial gain stages. The gain of each amplifier is con-
trolled by the AGC voltage. The global AGC range
is more than 60dB. Thanks to the internal AC
coupling no DC feedback is required.
Demodulation
It is a quasi-synchronous type with passive carrier
regeneration done by an external tuned circuit, and
a limiter amplifier.
Video Amplifier
The video amplifier provides a 2VPP video signal to
the output with a good phase and amplitude fre-
quency response.
White and Black Noise Inverter
A fixed 3.2V level is inserted when a white spot
above 4.5V (measured on the video output Pin 18)
happens, this prevents from very noisy signal on
the screen.
A fixed 2.5V level is inserted when a black spot
below 1.3V happens, this to avoid synchronization
on parasitic signals.
AGC Circuit
The AGC detector operates on top sync level, an
external capacitor on Pin 24 controls the time con-
stant.
The voltage on this capacitor is converted into a
current to control the amplifier stage.
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